President Obama gave no indication that the U.S. will relent in its air campaign against the Islamic State following the brutal murder of American reporter James Foley.

“We will be vigilant and we will be relentless,” Obama said on Wednesday. “When people harm Americans anywhere, we will do what’s necessary to see that justice is done.”

U.S. intelligence officials have authenticated video released on Tuesday by the Islamic State that shows a masked man decapitating Foley in retaliation for U.S. airstrikes in Iraq. At the end of the video, a militant warns that another American hostage, journalist Steven Sotloff, could be killed if airstrikes continued.

A Defense Department official confirmed that the U.S. has launched further airstrikes since the video was posted.

In a five-minute speech on Wednesday, Obama vowed that the U.S. “will continue to do what we must do to protect our people.”

While outwardly calm during the speech, Obama’s anger came through, especially when he condemned the Islamic State, formerly known as the Islamic State of Iraq and the Levant.

“ISIL speaks for no religion,” he said. “Their victims are overwhelmingly Muslim and no faith teaches people to massacre innocents. No just God would stand for what they did yesterday and what they do every single day. ISIL has no ideology of any value to human beings. Their ideology is bankrupt.”

Foley went missing in Syria two years ago. His mother released a statement on Tuesday that was posted on Facebook.

“We have never been prouder of our son Jim. He gave his life trying to expose the world to the suffering of the Syrian people. We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria or anywhere in the world.

“We thank Jim for all the joy he gave us. He was an extraordinary son, brother, journalist and person. Please respect our privacy in the days ahead as we mourn and cherish Jim.”